feat(test): add travis and cargo fmt script

.travis.yml

@@ -0,0 +1,17 @@
+language: rust
+sudo: false
+cache:
+  cargo
+rust:
+  - stable
+  - beta
+  - nightly
+before_install:
+  - bash ./tests/scripts/rustfmt.sh
+
+script:
+  - cargo fmt -- --write-mode diff
+  - cargo test
+matrix:
+  allow_failures:
+    - rust: nightly

tests/scripts/rustfmt.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+which rustfmt > /dev/null
+
+if [[ $? -ne 0 ]]; then
+  cargo install rustfmt
+else
+  current_version=$(rustfmt --version | cut -d '-' -f 1 | xargs)
+  upstream_version=$(cargo search rustfmt | head -n 1 | cut -d ' ' -f 3 | tr -d '"' | xargs)
+  if [ $current_version != $upstream_version ]; then
+    cargo install rustfmt --force
+  fi
+fi